Microscope: Birds on a wire

Double Helix magazine is looking for your questions! Our Microscope column answers the most intruiging science, tech, engineering and maths queries you can throw at us.

Comment on this post with your question, or email us at Helix.Editor@csiro.au. The best questions will be published in our magazine! Here’s a sample question to get you thinking.

Kyouka asks: How can birds sit on electrical lines without being electrocuted?

When it comes to describing electricity, there are three words you need to know – current, resistance and voltage.

Current is how many electrons are zipping by every second. Resistance describes how hard it is for the electrons to move. And voltage is a measure of the tug of war over the electrons between two points.

Imagine a super-strong team of people tugging hard on a rope. If they didn’t have much resistance, the rope would slide quickly through their hands and have a fast current.

A bird sitting on a power line isn’t part of the voltage tug of war inside the wire, so it’s fairly safe … unless it sits on two wires! If that happens, it can create a ‘short’ circuit. The bird becomes part of a new tug of war, where the electrons are pulled down one wire, through the poor bird, and into the second wire.

Sometimes, if a difference in voltage between any two points is big enough, a short circuit can form through the air and reach the ground. So it’s a good thing powerlines are high overhead or underground. Always stay clear – and leave them to the birds.

Answer written by Mike McRae

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